This invention relates to a process for preparing aliphatic hybrid ester/ether polyols. This process comprising simultaneously (A) transesterifying, and (B) alkoxylating (1) a mixture of (a) at least one ester group containing compound and (b) at least one hydroxyl group containing compound, with (2) one or more alkylene oxides, in the presence of (3) a mixture of catalysts that comprises (a) at least one DMC catalyst and (b) at least one non-alkaline transesterification catalyst. Such aliphatic hybrid ester/ether polyols can be used to produce polyurethane foams with a wide variety of cell structures, hardnesses and physical properties.
Polyether polyols are typically made from alkoxylating polyhydric hydroxyl-containing compounds with alkylene oxides such as propylene oxide (PO) and ethylene oxide (EO). Common polyether polyols which are useful for the production of polyurethane foam span a wide range of hydroxyl numbers from under 12 to over 900.
Polyester polyols are typically made from the condensation of one or more diacids or the anhydrides thereof, with dialcohols, though mixed or higher functionality may be employed for either the acid or alcohol containing compounds. In some cases reactants employed may contain both acid and alcohol functional groups in a single monomer compound. To be made well, polyester polyols require careful control of the addition of the reactants and precise dehydration to drive the esterification reaction to completion. Polyester polyols useful for the production of polyurethane foams may span a wide range of hydroxyl numbers from under 10 to over 700.
Very thorough reviews of the processes and products which have been investigated and developed to date for polyether and polyester polyols are provided in the monograph by Mihail Ionescu entitled “Chemistry and Technology of Polyols for Polyurethanes” (Rapra Technology Ltd., 2005); and for the polyols made by various reactions of acyl triglycerides, e.g., vegetable oils, in the review paper by Myriam Desrouches, et. al. called “From Vegetable Oils to Polyurethanes: Synthetic Routes to Polyols and Main Industrial Products,” (Polymer Reviews, 52: 38-72, 2012; Taylor and Francis Group LLC, publishers).
An object of the present invention was to overcome the limitations in the prior art and to provide an effective and efficient process for preparing aliphatic hybrid ester/ether polyols. A process which simultaneously transesterifies and alkoxylates a mixture of ester group containing compounds and hydroxyl group containing compounds with alkylene oxides using a dual catalyst system is not described in the prior art. It has been found that the process described herein forms aliphatic hybrid ester/ether polyols which do not require work-up and do not contain catalyst residues in the system that interfere with polyol-isocyanate reactions. The catalysts required by the novel process are essentially “pH-neutral” and, as such, do not interfere with urethane catalysis in flexible foams.